Method of making sound absorbing material



Exam' CROSS REFERENCE comPosxTloNS;

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COMING 0R mmv* 91 Sept. 8, 1942.

mamon oF MAKING sounn ABsoaING MATERIAL s. B. BRQwN rsi-AL Original Filed July 14, 1939 INVENTOR.

Gio/m5 5. BROWN BY ATTORNEY Patented Sept. 8, 1942 lMETHOD O MAKING SOUND ABSORBING MATERIAL George B. Brown, Martinsville, and Osborn Ayers,

Plainfield, N. J., assi Corporation, New Yor New York gnors to Johns-Manville k,

N. Y., a corporation of Original application July 14, 1939, Serial No.

284,390. Divided and this application November 12, 1941, Serial No. 418,720

v claims., V(ci. :a5- 155) The present invention relates to acoustical material, and particularly to a method of making monolithic sound-absorbing blocks or sheets, the instant application being a division of our application Serial No. 234,390, filed July 14, 1939, cov-l ering the product.

Acoustical treatments for application to the ceilings and walls of rooms and the like are at A present in wide commercial use. Such treat-v ments conventionally comprise sound-absorbing media applied as a iinishing or covering layer to the ceiling or room walls. Heretofore, however, there has not been obtained a low cost acoustical treatment in which is combined high sound-absorption emciency with the appearance and ease of application of monolithic panels or blocks. i

A principal object of the present invention is the provision of a method of making a monolithic acoustical block adapted for ready appliiv cation to a ceiling or wall by means of adhesives or suitable suspension means and which exhibits a high sound-absorbing efficiency.

A further object of the invention is the provision of a method of making a panel or a block., as referred to above, which is relatively inexlpensive as compared to sound-'absorbing structures heretofore employed for like uses.

A still further object of the invention is the provision of a method of making a sound-ab'- sorbing monolithic panel or block which is fireresistant, is not subject to warping or expansion when exposed to high humidities, can be painted without detracting from its acoustical properties, and which is of suiicient strength to readily withstand the handling necessary in its transportation and application.

Briefly stated, our method produces a monolithic product comprising porous sound-absorbing particles, particularly ground natural sponge, asbestos reinforcing bre, and a binder of the type of Portland cement. Such product is relatively low in cost, 'of the desired porosity, has a high sound-absorbing efficiency, and otherwise meets the several desiderata set forth in the statements of object above.

The method includes dry mixing the several ingredients and depositing the mixture on flanged mold boards to a depth slightly greater than the height of the anges. a sufficient amount of moisture to hydrate the vcernentitious binder, the material is slightly pressed and the mold boards are then stacked After wetting lwith the superposed boards to a finished thickness determined by the flanges. After the air curing, the slabs are preferably dried at elevated temperatures.

Our invention will be more fully understood and further objects and advantages thereof will become apparent when reference is made to the more detailed description thereof which is to follow and to the accompanying drawing, in which:

Fig. 1 is a fragmentary perspective view of an acoustical panel or block formed in accordance with the invention;

Fig. 2 is a detail sectional view on an enlarged scale taken on the line '2-2 of Fig. 1;

Fig. 3 is a diagrammatic view, partially in elevation and partially in section, of an apparatus employed with the instant invention;

Fig. 4 is a perspective view of a mold board employed with the apparatus'of Fig. 3;

' Fig. 5v is a sectional view on an enlarged scale taken on the line 5-5 of Fig. 3; and

Fig. 6 is an elevational view of a'plurality of Athe mold boards of Fig. '4 'in stacked relationship. "Referring now to the drawing, and particularly to Figs. 1 and 2, a sound-absorbing panel or slab I0V is illustrated comprising ground soon e particles Il, asbestos'iibres' l2, and a Binder, preithe ype o ort and cement i3. `Suitably, the sponge' is-natural sponge 'which has been washed and subdivided as'by grinding into to permit the cementitious material to air cure fand to compress the mixture by the weight of f" small particles of-asize, say, to pass a mesh screen. In lieu of` natural sponge, artificial sponge may be employed. As stated, the cementitiousfmaterial-is preferably Portland cement and the 'description will be direc e o a mel o employing this material as a binder. However, there may be employed other types of binders,

such as ox sul hate cement, aluminous cement, silicate of soda, gypsum, and the like.

e sponge particles Il are present in sufficient amoun Alse a substantial proportion of the bulk of the panel, the cement and asbestos. iibre serving, in eect, as a skeletonizing structure, retaining the particles in the panel form. The panel is of high porosity and soundabsorbing efficiency, due to the voids of the sponge particles and those formed by the skeletonized binder structure between the particles. As will be understood by those skilled in the art, the relative proportions of the sponge, fibres, and cement may be varied within limits, depending upon the emphasis desired on any of the Iparticular properties of the sound-absorbing panel. Thus, for example, increasing the proportion of the CUATING R PLASTlC nay 5B SEalted, hOWeVEI, Ol purposes Of eX- emplication that a highly suitable panel has been obtained by employing a mixture comprising by weight ground sponge 13.40%, asbestos CROSS REFERENCE bre 8.85%, and 'Big5 early strength Portland cement 77.75%.

will be observed particularly from an examination of Fig. 2, the density of the panel is preferably made somewhat greater adjacent the under-face, that is, the face opposite to the surface I6 which is to be the face of the panel exposed to the sound to be absorbed. By this construction, the greatest porosity is achieved at the exposed face, with the panel progressively becoming denser as the opposite face is approached. Sound-absorbing materials having such characteristics have been found to be particularly effective. The corners of the face I6 may be suitably beveled as illustrated at I4, whereby when the panels are secured to a wall or ceiling surface, as by adhesive, suspension means, or the like, an attractive tiled appearance is presented to the observer.

Panels as described above may be formed by either manual or machine operation. However, a machine operation is preferred and for purposes of exempliication suitable apparatus for this purpose is illustrated in Figs. 3, 4 and 5. The apparatus comprises a mixer of any suitable type which includes paddle members 22 secured to a rotating shaft 24. The ground sponge, fibre, and cementitious material, all in dry form, are deposited in the desired proportions in the mixer discharged through a valve 25 into a bottomless hopper 26 supported above the upper reach 30 of an endless conveyor belt 28. The conveyor is arranged to travel in the direction indicated by the arrows on rolls 34 driven by any suitable means (not shown).

A plurality of mold or caul boards 40 are provided, each comprising a base member 42, longitudinally extending side nanges 44, which may suitably take the form of angle irons, and an end wall or ange 46. The ends of wall 46 are spaced from the side flanges as indicated at 4S, a distance slightly greater than the thickness of the material constituting the side walls 36 of hopper 26. Walls or anges 44 and 46 extend upwardly from the base member 42, a xdistance equal to the desired thickness of the acoustical panel to be formed.

The mold boards 40 are similarly positioned on the upper reach of the conveyor in end-to-end contiguous relationship, whereby the end wall 46 of one board forms, in eiect, an end wall of an adjacent board. The boards are carried by the belt beneath hopper 25. The side walls 36 of hopper 26 extend downwardly to substantially contact the bases 42 of boards 40 and are positioned to pass through the openings 48 between the end wall 46 and side walls 44 of the boards (see Fig. 5). The lower edges of end Walls 38 and 39 of hopper 26 are raised sufficiently to clear end wall 46 of the boards as they pass therebeneath, the lower edge of end wall 39 at the rearward end of the hopper being raised an additional distance to permit a thickness cf material 20 and thoroughly mixed and the mix is thenron the boards somewhat greater than the height of nanges 44 and 46.

Hopper 26 includes a material leveling device 50 comprising pulleys 52 driven from any suitable source of power (not shown), carrying an endless belt 54 traveling in the direction indicated by the arrow. The endless belt carries a plurality of vanes 55 extending the width of hopper 26 and slanting away from the direction of travel of the belt, as illustrated in Fig. 3. Suitably, the leveling device 50 is arranged for adjustment as to height. Rotation of belt 54 about the pulleys 52 causes the vanes 56 to level off the material on the caul boards at a predetermined height and further serves to agitate the material in hopper 26, thus aiding in maintaining the proper intermixture of the several ingredients thereof. The backward slant of vanes 56 prevents any appreciable quantity of the material from being carried by the vanes to the rear of the leveling device.

A smoothing roll 60 may be provided adjacent hopper 26, the smoothing roll being suitably perforated as indicated at 62. Spray heads 64 are located above the travel of conveyor 28 and are arranged to spray water or other wetting medium on the layer of material carried by the mold boards as they pass therebeneath, the boards then passing under a press roll 66.

The dry mix in the hopper 26 fills the caul boards 40 as they pass therebeneath to a depth as determined by leveling device 50. suitably, the depth of the material is somewhat greater than the height of the flanges 44 and 46 of the caul boards. The loaded boards are then carried beneath smoothing roll 60 and to spray heads 64. The flow of water from the spray heads is controlled to provide a sufficient amount to wet the mix and hydrate the cement without leaving any substantial excess of water. A plurality of the spray heads are preferably used as indicated in the drawing in order that the quantity of water issuing from each head in a given time will not require a spray of such force as would wash any substantial quantity of the cement from the surface of the layer into the interior thereof. After the mixture on the mold boards is wetted, the same is pressed down to some extent by press roll 66, the depth of the material, however, still being preferably somewhat greater than the height of the flanges of the caul boards. The boards are then stacked, as indicated in Fig. 6, and the binder permitted to air cure for a period, say, of three days.

During the air curing, the weight of the stacked boards, a suitable weighting device 1D preferably being employed over the layer 0n the uppermost board, serves to compress the material thereon to a depth equal to the height of the flanges 44 and 46. In other words, the material is compressed until the bottom of each mold board rests upon the anges of the one therebeneath. After the air curing, the mold boards are separated and the units are transferred to a o suitable kiln and the material thoroughly dried at a temperature, say, of 250 F. for approximately 24 hours. After the curing and drying steps, the panels are removed, cut to any suitable dimensions, an-d preferably beveled as indicated at I4 in Figs. 1 and 2. Thereafter, the panels may be painted or lacquered if desired.

The compressing of the material to a uniform thickness in the manner described above eliminates surface sanding or other similar surface treatments, with consequent simplification of the L nulnnlul operation and also with preservation of the preferred natural appearance ci the panel. Also, by the described method, the material adjacent the upper face of the layer on the mold board, which is preferably to be the under-face of the nished panel, is compressed to a greater density than the remainder of the layer to provide the increased density in this portion of the panel, previously referred to. The increased density of the block adjacent the under-face is illustrated particularly in Fig. 2. As will be understood, although due to the greater compression adjacent this face there will be a greater concentration of both the sponge and asbestos, at the same time the number and the size of the voids between the particles and the libres will be decreased with a resultant overall increase in density.

Having thus described our invention in rather full detail, it will be understood that these details need not be strictly adhered to, but that various changes and modifications will suggest themselves to one skilled in the art, all falling within the scope of the invention as defined by the subjoined claims.

What we claim is:

1. A method of making a monolithic soundabsorbing unit comprising dry mixing ground sponge, asbestos fibre, and cement, depositing the mixture in a uniform thickness layer, wetting the deposited mixture to hydrate the cement, slightly compressing the layer, and air curing the cement while maintaining pressure on the layer until the layer assumes a predetermined thickness.

2. A method of making a monolithic soundabsorbing unit comprising dry mixing `ground sponge, asbestos bre, and cement, depositing the mixture in a uniform thickness layer, wetting the deposited mixture with sumcient Water to hydrate the cement, slightly compressing the layer, air curing the cement while maintaining pressure on the layer until the layer assumes a predetermined thickness, and then oven drying said layer.

3. A method of making a monolithic soundabsorbing unit comprising dry mixing ground sponge, asbestos bre, and Portland cement, depositing the mixture in a uniform thickness layer, wetting the deposited mixture with suiicient water to hydrate the cement without the presence oi a substantial excess of water and in a manner to prevent substantial washing of 'the cement from a surface of the layer, air curing the cement while maintaining pressure on the layer until the layer assumes a predetermined thickness, and then oven drying the layer.

4. A method of making a monolithic soundabsorbing unit comprising dry mixing ground sponge, asbestos bre, and Portland cement in proportions of the order of sponge 13,40%, asbestos bre 8.85%, and cement 77.75%, depositing the mixture in a uniform thickness layer, wetting the deposited mixture with a suiicient amount of water to hydrate the cement without the presence of a substantial excess of water, slightly compressing the layer, air curing the cement while maintaining pressure on the layer until the layer assumes a predetermined thickness, and then oven drying said layer.

6. A method of making a monolithic soundabsorbing unit comprising dry mixing ground sponge, asbestos fibre, and cement, depositing the mixture in a uniform thickness layer, wetting the deposited mixture, applying pressure to the layer at one surface thereof, and air curing the cement while maintaining pressure on said surface to cause the layer to assume a predetermined thickness.

7. A method of making a monolithic soundabsorbing unit comprising dry mixing ground sponge, asbestos bre, and cement, depositing the mixture in a uniform thickness layer on a mold board including thickness gauging means, leveling the deposited mixture to form a layer of a depth greater than the height of the thickness gauging means, wetting the deposited mixture, slightly compressing the layer, air curing the cement while maintaining pressure on the layer until the same assumes a thickness determined by said thickness gauging means, and then oven drying said layer.

GEORGE B. BROWN. OSBORN AYERS 

